338 Lapua Mag pressure signs?

[pgv5705]

Experiencing high pressure signs (sticky bolt, extractor marks, etc) at what should be reduced loads and a I am a bit stumped? Looking for advice.

The rifle has a Stiller Tac-338 action and 30" Broughton bbl (1-10)

300 grain SMK's
Lapua brass (new)
FGMM215 primers
Mag Length (.075 jump)
Retumbo

I have been as low as 87 grains of powder and still experienced overpressure.

Has anyone experienced similar results when using Retumbo for 338 Lapua Magnum?

Also, my velocities seemed a touch low considering my barrel length.

 

[ChrisGarrett]

Re: 338 Lapua Mag pressure signs?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PViddy</div><div class="ubbcode-body">Experiencing high pressure signs (sticky bolt, extractor marks, etc) at what should be reduced loads and a I am a bit stumped? Looking for advice.

The rifle has a Stiller Tac-338 action and 30" Broughton bbl (1-10)

300 grain SMK's
Lapua brass (new)
FGMM215 primers
Mag Length (.075 jump)
Retumbo

I have been as low as 87 grains of powder and still experienced overpressure.

Has anyone experienced similar results when using Retumbo for 338 Lapua Magnum?

Also, my velocities seemed a touch low considering my barrel length. </div></div>

Retumbo is a top 338LM powder and those using it are Tier 1 all the way.

You can always try H-1000, RL-25, VV-170 and VV-N570 and see how she performs.

We need more info in the form of specifics.

Guessing as to why your rifle is shooting a moderate load and getting pressure signs is a waste of time and gets us nowhere.

Chris

 

[pgv5705]

Re: 338 Lapua Mag pressure signs?

I've already tried RL25 and US869 and both of those powders also showed pressure signs very early.

I've been loading my own for about 15 years now and this is the first rifle that I've had this problem with. I load several other heavy magnums, both custom built and factory, so this isn't my first venture into big guns.

Regarding Retumbo, I first tried a load that several of my associates were shooting in various rifles(dangerously assuming it would be safe in my rifle too) and it was great except for a slightly sticky bolt and extractor marks. 93 grs delivered 18fps extreme spread, 2860 fps average, and a standard deviation of 6. The accuracy was exceptional too, better than half moa at 714yds.

I am throwing my charges with a Lyman digital scale, and the brass is new Lapua that I neck turned and sized only (Redding type S dies). The O.A.T. on the day of testing was around 60 degrees Fahrenheit and at sea level.

The headspace in this rifle is a little generous, about .009" over minimum spec. I have completely disassembled the bolt for cleaning and inspection and found nothing unusual.

I am also looking at velocity very closely. It doesn't seem correct that a 338 LM shooting Retumbo and 300gr pills through a 30" bbl is only capable of around 2600fps before the bolt starts to stick.


Suppose I am just frustrated because I had higher expectations for this stick.

 

[cali_tz]

Re: 338 Lapua Mag pressure signs?

with my Rem 700 338LM, I was also surprised at the low muzzle velocities, so much so that I switched to my Rem 700 308 to check my chrono and make sure it was still recording correctly.

This was using VV560, and I was measuring 200fps less than the VV reloading guide. I maxed out at ~2600fps using VV's max load, for which they predicted 2800fps.

However, even at VV560 max recommended load, I still saw no hints of pressure. Using both once fired Hornady and Lapua brass.

 

[pgv5705]

Re: 338 Lapua Mag pressure signs?

I will test again tomorrow with charges at the lower end of the spectrum (85-89) and I will publish the velocities and the exact charge weight where excess pressure begins.

Then perhaps someone will be able to verify my findings as either normal or abnormal.

PV

 

[oneshot onekill]

Re: 338 Lapua Mag pressure signs?

I posted a similar thread some months ago and was told that you can actually have signs of over-pressure or can even damage your rifle if the powder charge is too little. I don't know the physics of that but it left me scratching my head... FWIW